Real time messaging with websockets

• WebSocket is a thin, lightweight layer above TCP. This makes it suitable for using subprotocols to embed messages.

• STOMP is a subprotocol operating on top of the lower-level WebSocket.

• Gradle dependencies:

dependencies {
	implementation 'org.springframework.boot:spring-boot-starter-websocket'
	testImplementation 'org.springframework.boot:spring-boot-starter-test'
    implementation 'org.webjars:webjars-locator-core'
    implementation 'org.webjars:sockjs-client:1.0.2'
    implementation 'org.webjars:stomp-websocket:2.3.3'
    implementation 'org.webjars:bootstrap:3.3.7'
    implementation 'org.webjars:jquery:3.1.1-1'
}

Create a Resource Representation Class

• The service will accept messages that contain a name in a STOMP message whose body is a JSON object.ex:

{
    "name": "Fred"
}

• Create java class with getname() method.

• Create java class with getContent() method.

• Create a Message-handling Controller:

@Controller
public class GreetingController {


  @MessageMapping("/hello")
  @SendTo("/topic/greetings")
  public Greeting greeting(HelloMessage message) throws Exception {
    Thread.sleep(1000); // simulated delay
    return new Greeting("Hello, " + HtmlUtils.htmlEscape(message.getName()) + "!");
  }

}

• Configure Spring for STOMP messaging:

@Configuration
@EnableWebSocketMessageBroker
public class WebSocketConfig implements WebSocketMessageBrokerConfigurer {

  @Override
  public void configureMessageBroker(MessageBrokerRegistry config) {
    config.enableSimpleBroker("/topic");
    config.setApplicationDestinationPrefixes("/app");
  }

  @Override
  public void registerStompEndpoints(StompEndpointRegistry registry) {
    registry.addEndpoint("/gs-guide-websocket").withSockJS();
  }

}

@EnableWebSocketMessageBroker enables WebSocket message handling, backed by a message broker.

• Create a Browser Client: The html file will import, SockJS and STOMP javascript libraries that will be used to communicate with our server through STOMP over websocket. as shown:

 <script src="/webjars/sockjs-client/sockjs.min.js"></script>
    <script src="/webjars/stomp-websocket/stomp.min.js"></script>